English leaves are made to fall, as from the first they are nearly divided from the petiole or leaf stalk, the mark of division being to be seen in the budding leaf.
Have our Australian leaves that mark?
No, they have not. The petiole expands or becomes leafy, and the leaves, therefore, do not readily fall. There is yet another difference. While the glands or tumours for imbibing moisture are on the underside of the leaf in England, they are on both sides of it here. Instead, too, of being horizontal, our leaves are set in edgewise on their stems.
I often notice the great difference there is in leaves, father.
Yes, they differ in size, structure, direction of veins, situation, form, duration, kind of surface, &c.
But what have you to say of those plants which have no leaves? I could never see any in our sheoak nor cherry.
Quite true. Our Casuarina or oak family, and the Exocarpus, or cherry, have no leaves. They have, however, long hanging knotted twigs at the end of branches. They have been called the Pines of Australia.
Is light necessary to leaves as well as air?
It is. Sunlight acts chemically to produce changes in substances. It is believed necessary to enable the leaf to separate the carbon from the oxygen in carbonic acid gas. Leaves love light, and will turn toward it. Some even follow the sun in its daily motion. In a dark place, plants soon fade, and the leaf turns white.